In a nutshell…
If you have lots of links to your site, then Google/Bing/etc. assumes your site is full of important content that everyone is interested in then ranks your site higher in searches.
After recent updates, Google/Bing/etc. algorithms are now looking at the quality of the links, not just the quantity.
If you have links from reputable websites to yours then you will get better search results.
If you buy links from link farms and Google detects this, then your site will get demoted or even blacklisted.
My advice is don’t concentrate on link building, concentrate on good quality content – If you build it the links will come….
Hope this helps!
Regards,
